A liquid crystal display device including a liquid crystal panel has been used as a display device such as a mobile terminal device and a television device. The liquid crystal panel does not emit light and necessarily uses external light for displaying an image. Therefore, such a type of display device includes a lighting device (so-called backlight unit) other than the liquid crystal panel for supplying light to the liquid crystal panel. Such a lighting device is arranged on a back surface side of the liquid crystal panel and is configured to supply planar light, which spreads in a planar form, to the back surface of the liquid crystal panel.
There have been demands of high contrast of a display image or decrease of power consumption and technology of local dimming has been proposed. In such a local dimming technology, a light emission area is divided into multiple areas and brightness of the backlight unit is controlled for each of the areas. With the local dimming technology, high dynamic range (HDR) display that broadens brightness contrast is performed and high display quality is achieved.
The backlight unit is generally classified into a direct type and an edge light type according to arrangement of a light source. The direct type backlight unit includes the light, source directly below a display surface of the liquid crystal panel. The edge light type backlight unit includes the light, source beside the liquid crystal panel. The liquid crystal display device has been strongly demanded to be thinner and the edge light type backlight unit is preferably used to achieve further decrease of thickness.
There has been known a backlight unit of the edge light type with the local dimming technology.